Gear hob relieving device video long

For several years now I have been trying to make my own gear cutting hobs. The Eureka relieving device shown in Workshop Practice Series 17 is what I started with. They started with a picture of the Balzer device and reverse engineered it.

I followed the plans closely because I had no idea how it worked.

My first change was to make it longer so a hob blank would fit. The hobs for diametral pitch have a lead which is a factor of pi. I used a 42t and a 44t gear together to make 22/7 pi.

This makes the half nuts unusable like metric conversion gears do.To do plain turning on hob blanks the tool is pulled back and the lathe is reversed with the half nuts engaged for the next pass.

The problem with the Eureka relieving device is that it drives through a ratchet so it loses place when you reverse it.

I was able to relieve hobs with it but it was very tedious since the tool had to be adjusted to pick up the thread each pass.

My solution is to use a pattern thread on the reliever and a half nut connected to the lathe saddle to drive the carriage.

Now the lathe is only reversed while cutting the pattern thread and half nut. A different pattern and nut are needed for each thread pitch.

Plain turning the hob and relieving it are all done with the pattern thread so there is no need to reverse the lathe. The pattern thread half nut always engages correctly.

A plain arbor that matches the reliever arbor is used. Both have a keyway to index the pattern thread and hob blank.

There is a better description of the Balzer Relieving device at

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pages 26 to 28 which seems to be the origin of this tool in 1896 or so.

Taylor's 1906 patent 817885 is a paraphrase of Balzer's design.

Balzer has a 1895 patent 535127 for a reliever with no ratchets and a trick gear but it was not the design that he manufactured.

Here is my hob reliever on U-tube. It is not as complicated as building a backing off lathe but it can't do small hobs for cutting worm wheels.

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So far I can't get U-tube search to find it.

Best Regards Charlie

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Great video!

That's the best Video of a Eureka style reeiving tool that I have seen.

Nice to see a video that's long enough to get a decent look, too.

If you can, edit the title to something like "A Eureka style gear hob relieving attachment" so it will get found by guys looking for those terms, together or in combination.

Same with your description. Use words or phrases that will lead the search engine in to your video. Few will search for "gears hobbing" but "gear hobbing" will get them closer. Suggest the words "gear" and "cutter" get added into the tags if you can.

Nice trick with the master thread to get the pitch for the hob. How tricky is it to get the master in synch with the hob blank?

Cheers Trevor Jones

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Trevor Jones

Thanks Trevor, I will try to get the search terms better. Even the exact title did not show up.

After the plain turning is done the the hob blank is blued and put on the reliever and marked on the end with a cutter bit as it turns. The pattern screw is marked so the two parts can be put on the reliever the same way they were during plain turning. Both arbors have a keyway.

The mark on the hob blank looks like a circular saw. This shows where to put the gashes. Since the beginning of the teeth are not perfectly formed as slack is being taken up at the start, the gashes should be as small as practical. Later the odd parts will be cut away and the gash made wider.

The tops of the hob teeth are relieved with a straight cutter first. I blue the hob blank to be able to see how the cutting is going.

Then the thread relieving cutter is adjusted to pick up the thread once and then stays in synch. Small adjustments can be made on the pivot screws of the follower that carries the nut.

This is the first time for me on U-tube. Charlie

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Very impressive project. I remember reading about the eureka and thinking it was too big a job for me to take on. Do you know about how many hours you spent on construction?


Reply to
Karl Townsend

Karl, The original Eureka was said to have been made in four days. My first longer version was done over a period of two weeks. The plates were made using a rotary table and boring head a lot while following the plans closely. Holding the parts is the hardest thing to do.

The main arbor has three offsets that make it tricky. I used extra length at the ends so two sets of centers could be milled off and the relieving centers then drilled. The offset is only .030" so it must be done later.

The Eureka described in Workshop Series 17 has the curves of Balzer's

1896 reliever that inspired it. My second version with the pattern thread just needed still longer parts and used the Eureka mechanism to drive it. My half nut carrier has no curves at all.

The Balzer has only one ratchet and uses friction washers to keep it from freewheeling when not being turned by its ratchet. The Eureka has a second ratchet that seems like an after thought to do this. I have a cork friction washer and Eureka's ratchet on mine.

I am cutting A2 steel with broad flat topped cutters making my hobs so I can't take much of a cut. They have a 7/8" bore and a 1/8" keyway.


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